Add uv2nix to build Python packages from uv.lock. This creates a fully
Nix-managed Python environment with the Rust bindings injected via overlay.
Changes:
- Add pyproject-nix, uv2nix, and pyproject-build-systems flake inputs
- Create python/parts.nix with overlays to inject Nix-built Rust wheel
- Export packages.exo on macOS (wraps exo/exo-master/exo-worker with dashboard)
- Add checks.lint (ruff, all platforms) and checks.pytest (macOS only)
- Simplify CI typecheck job using nicknovitski/nix-develop action
- Delete .github/actions/typecheck composite action (no longer needed)
- Add no-build-package for MLX packages in pyproject.toml (use wheels)
The Python build is currently macOS-only since MLX requires Metal. Linux
support will be added once the pyproject dependencies are simplified.
Test plan:
- Run `nix flake check` on macOS to verify pytest and lint pass
- Build exo package on macOS: `nix build .#exo`
- Verify CI pipeline passes with simplified typecheck job
